Pilot light safety control apparatus



United States Patent 3,1l6,641 PILOT LEGHT SAFETY CGNTRL APPARATUS AND DETECTTG ASSEMBLY THEREFOR Asbury S. Parks, Houston, Tex., assignor to Dover Corporation, Tulsa, ltla. a corporation of Delaware Filed Apr. 21, 196i), Ser. No. 23,662 7 Claims. (Cl. 73-362.3)

This invention relates to new and useful improvements in pilot light safety control apparatus and relates particularly to an improved detecting assembly for use in such apparatus.

As is well known, heaters or furnaces utilizing gas as fuel include a main burner or burners which are operated in accordance with load conditions; where the load on the furnace is variable, the main burner is operated intermittently, that is, the burner is fired for a period and is then idle for a period. In order to re-light the main burner upon each cycle, a constantly burning pilot light or flame is provided and so long as the pilot light remains lighted, operation is satisfactory; however, if the pilot light or ilarne is extinguished, then re-ring of the main burners cannot be accomplished should gas flow again be conducted to the main burner. In such instance, gas may flow into the lirebox of the heater or furnace and may collect in such volume as to create a real hazard of explosion, this being particularly true where heaters or furnaces are in operation in isolated locations as in the case in oil and gas fields.

To eliminate the hazards incident to pilot light outage, various safety control devices have been used to detect such outage and normally operate to shut off flow of fuel gas to the main burner. These devices employ a temperaturesensitive detecting means which is located to be heated by the pilot light flame, whereby said means is exposed to excessive heat. Such exposure results in destruction of the material of which said means is constructed in a relatively short period of time thereby rendering the same inoperative. Furthermore since a pilot light flame is relatively small, the heat thereof is concentrated upon only a relatively small area of the temperature sensitive means with the result that only a relatively small motion can be obtained by the physical changes in said means, as caused by the temperature change due to pilot outage. Where only such relatively small motion is available, the adjustment of any actuator becomes diticult and is in fact so sensitive that operation becomes unreliable.

It is, therefore, one object of this invention to provide an improved pilot light safety control apparatus which overcomes the disadvantages of the devices presently available on the open market.

An important object is to provide an improved detecting element assembly for pilot safety control apparatus which is so constructed that it may be placed directly in a high temperature pilot light llame without danger of destroying the metals used in its construction whereby said assembly will operate efficiently over long periods of time.

A particular object is to provide an assembly, of the character described, wherein the temperature sensitive or responsive means is surrounded by a heat conducting member which functions to conduct heat away from the zone of pilot llame heat application and also acts to distribute said heat substantially evenly along the length of the temperature responsive means, whereby overheating of the zone of heat application is prevented and also whereby the entire length of the temperature sensitive means is available to function as a heat sensing unit.

Another object is to provide an assembly, of the character described, wherein the heat conducting member which surrounds the temperature sensitive means is constructed of material which would be damaged if directly exposed to the pilot light flame and wherein said member is protected against such damage by a llame-resistant shielding means which encloses the member and is sealed in such manner that oxidation of the heat conducting member and resultant damage or destruction thereof is prevented.

Still another object is to provide an improved detector assembly having a bi-metallic temperature sensitive element constructed of metals having different coeicients of thermal expansion; one of said metals having a relatively constant rate of expansion with increasing temperature, with the other metal being a low expansion alloy having the characteristic of low rate of expansion within the lower temperature ranges and having an increasing rate of expansion in the higher ranges, whereby operation of the element within the lower temperature ranges produces a relatively high rate of differential expansion between said metals. The assembly also including means for transferring the heat away from the zone of heat application and for distributing said heat over the length of the bi-metallic element in such manner that the overall temperature of the bi-metallic element is maintained preferably within the lower temperature ranges wherein the rate of differential of expansion is high to thereby assure rapid response to pilot light outage.

A particular object is to provide a temperature sensitive means, of the character described, which lends itself to combination with various types of operating control units for controlling the ow of a fuel gas to the main burner of a heater or furnace.

The construction designed to carry out the invention will be hereinafter described, together with other features thereof.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof wherein an example of the invention is shown, and wherein:

FGURE 1 is a longitudinal, sectional view of a pilot safety control apparatus including the improved detector assembly constructed in accordance with the invention, and showing the same combined with a pilot pressure control unit; the main burner and the various lines and valves being illustrated schematically;

FIGURE 2 is a transverse, sectional view taken on the line 2 2 of FIGURE l; and

FIGURE 3 is a chart illustrating the thermal expansion characteristics of the materials, which are preferably used in the construction of the bi-rnetallic temperature sensitive element.

in the drawings, the improved detecting element assembly pilot light safety control apparatus is generally designated by the letter A and includes a body 10 having an axial bore ll which is counterbored at 12. The body may have one end provided with threads 13 rwhereby it may be readily connected to a control unit which is shown as a pneumatically operated unit and which is generally designated by the letter B. The opposite end 14 of the body il@ may be reduced in the manner illustrated in FIGURE l.

A temperature-sensitive or responsive element T is `secured to and projects from the reduced end of lthe body lil and includes an inner rod l5 which extends into and through the bore il and counterbore l?. of the body. The element T also includes a relatively thin metallic tube le which surrounds the projecting portion of the rod 1S and which has one end thereof extending into the bore il of the body. The tube i6 is secured as by welding l? to a collar at the reduced end 14 of the body and is immovable with respect to the body. The outer end of the `tribe la terminates adjacent the end of the actuating rod 15 and lis suitably welded or othenwise secured thereto at 13. That end portion 15a of the rod 15 which is opposite the portion surrounded by the tube 16 may extend entirely through the body 1i) and may be threaded for connection to the operating parts of the control unit B. As will be explained, the rod 15 forms an actuator or operating member.

The rod 15 is constructed of a metal having a different coeicient of expansion than does the metal of the relatively thin surrounding tube 16, whereby, when the temperature of the rod 15 and tube 16 are changed to a similar degree, there is a corresponding change in their relative lengths. Since the tube is fixed to the body at 17 while the rod is free to move with respect to said body, variations in `temperature will result in imparting motion to that end a of the rod which is remote from the tube. The Irod and tube thus form the lai-metallic temperature-sensitive or responsive element T and as will be explained, the motion of the actuator rod 15 as produced by temperature changes acting upon said temperature-sensitive element, may be utilized to properly control the ow of a fuel gas to a main burner.

A tubular sleeve or member 19, which functions as a heat-conducting or heat-distributing member, encircles the temperature responsive element T and extends substantially throughout the length thereof. The sleeve has a relatively thick wall and the metal of which it is made has a very high heat conductivity; the bore 19a of said sleeve is larger than the exterior of the tube 16 to provide an annular air space between said tube and the sleeve. The heat-conducting or distributing sleeve 19 is enclosed within a thin-walled shield 20 which is formed of a material, such as stainless steel, capable of withstanding a relatively high temperature over an indefinite period of time. The tubular shield 20 has one end seal-welded at 21 to the body and has its opposite end closed by an end plate 22 whereby the temperature responsive element T, as well as the sleeve are protected against damage due to oxidation. It will be noted that the heat conducting sleeve 19 is not fixed within the bore of the shield 20 but rather is free oatng or movable longitudinally Within limits within said shield to allow for expansion and retraction of the sleeve under varying temperature conditions.

When the assembly is in use, the pilot llame indicated at F is acting on one area or zone of the heat resistant shield 2t) of lthe assembly. :From the point of heat application heat immediately starts to flow into the relatively thick-walled heat conducting sleeve or member 19. Since the sleeve 19 has a relatively enormous capacity .to carry heat, the heat flows axially down this element and longitudinally thereof toward the cooler region outside of the direct pilot light flame whereby heat is continuously conducted away from the area at which heat is being applied. This constant conduction of heat from the zone of heat application functions to prevent overheating `of those portions of the shield 20, sleeve 19 and the temperature-sensitive element T, which portions are immediately adjacent the direct flame. At the same time, the sleeve or member 19 distributes the heat Substantially evenly throughout its length and said heat is transmitted or distributed across the air space to the temperature responsive element T, whereby substantially the entire length of the element T is heated `to subject its full length to motion in response to temperature. This results in greater movement of the actuator rod 15a than would be possible if only a small pilot flame is acting upon only one localized section of the temperature responsive element. Where increased `or amplified motion of the actuator is produced more reliable operation of a control unit may be effected. The arrangement thus provides a relatively large or elongate temperature sensitive element, the entire length of which efciently functions as a sensing element.

Where a small temperature-sensitive clement or only a portion of a larger temperature-sensitive element is inserted in the pilot light flame, such small member is heated to a given temperature at only one point and very little heat escapes the device in such flame while heating is occurring. In the present assembly, heat is applied to one end or one zone thereot` and this heat is constantly conducted away from `the point orr heat application. This heat travels axially along the element to a region ontside the flame Where it continuously escapes so that with the present invention there is a constant heat input to sleeve 19 and a constant heat loss from said sleeve. The net temperature of the temperature responsive element T is the result of the difference in this constant input and loss of heat from the system. So long as heat is being applied, the tube 16 of the element T will have elongated and will have moved the actuating rod 15 in a direction to the right in FIGURE 1. If the flame F should be extinguished, the heat input to the device is immediately halted, but the heat loss is continued. This produces a relatively rapid rate of cooling of the temperature-sensitive element T thereby decreasing the time of response after the flame outage to provide a rapid response unit. Upon cooling the tube 16 will contract and the actuating rod 15a is moved in a direction to the left in FIGURE l. With the protection of the heat conducting sleeve 19, the temperature of the temperature-sensitive element T cannot be excessively raised by the piling up of heat from the flame because the heat is constantly carried away from the point of heat application and is distributed over substantially the entire area of said temperature responsive element.

With the foregoing construction one end or section of the device may be placed directly in the pilot flame and because heat is being constantly carried away from this zone there is no danger of destroying the temperature responsive element T through excessive heat application in a localized area, as would be the case if the heat conducting member 19 and shield 2t) were not employed. Furthermore, designs of various heaters and tire-boxes may dictate that the temperature-sensitive element T be relatively long as compared to the part which is within the pilot fiame and the present assembly makes the entire length of an elongate temperature sensitive element effective as a sensing device.

As has been described, the temperature-sensitive element T is constructed of the inner rod 15 and the outer tube 16 and these members of the element are constructed of metals having different co-eflicients of expansion so that each expands and contracts at a different rate under a given temperature condition. Although various metals may be employed it is preferable that the metal of which the inner rod is constructed be a low expansion alloy, examples of such alloy being available on the open market under the trade names Invar and Nilvan A low expansion alloy has the characteristics of a low rate of thermal expansion Within the lower temperature range with a greatly increasing rate of expansion in the higher temperature ranges; in fact, within the higher temperature ranges, the rate Iof thermal expansion approaches that of the stainless steels which have a relatively constant rate of thermal expansion. The outer tube 16 is preferably constructed of a metal, such as stainless steel, which has a substantially constantly increasing rate of expansion with increasing temperature.

The chart, FIGURE 3, illustrates the rate of expansion in thousandths of an inch of the rod 15 and tube 16 under increasing temperature condition where said rod is constructed of a low expansion alloy and the tube is constructed of stainless steel. The inclined line L represents the rate of thermal expansion of the tube 16 and shows that as temperature increases, the rate of expansion increases in substantially constant rate to such increase in te-mperature. The action of the low expansion alloy of which the rod is constructed is indicated by line L-1; in the lower temperature range and up to the point l5 on the chart the rate 'of expansion of the rod 16 is relatively low but in the higher temperature range the rate of expansion increases sharply and as a matter of fact may thereafter equa-l the rate of expansion of the tube. Thus, in the lower temperature ranges there is a quickly varying difference in the ratio of thermal expansion of the rzod and tube, as caused by temperature changes, so that maximum movement of the actuator end 15a of the rod is effected in this range.

By enclosing the temperature-sensitive element T within the heat conduct-ing or distributing sleeve 19, the excessive heating o-f only one area of the element is eliminated and heat is continuously transferred away from the point of heat application. By selecting the proper wall thickness and length of the sleeve member 19 in relationship to the wall thickness of the shield 2t? and also in relationship to the size or area of the temperature responsive element T, the over-all temperature of the element T is maintained within the lower temperature range, that is, between point O and point P on the chart. This increases the sensitivity of the unit to changes in temperature even though part of the heat-sensitive element, being adjacent the pilot light tia-me, is constantly within a higher temperature range where ordinarily differential expansion of the rod and tube would be slight. It is also noted that when pilot light outage occurs, rapid response by motion of the nod occurs due to the high rate of differential contraction of the rod and tube.

The bi-metallic type of temperature-sensitive element T has been found satisfactory in operation but it is evident that other types of detecting elements, such as a gasfilled bulb, could be substituted therefor. The heat conducting and distributing sleeve 19 and shield 20 would enclose such other temperature-sensitive element and would function in the manner heretofore described to produce the improved results.

The device A may be combined in any desired manner with various controls which would shut off the flow of gas into a main burner when and if the pilot flame F is extinguished. In FIGURE l the assembly A is illustrated as lcombined with a pilot pressure control unit B which controls the fiow of fuel gas to `a main gas burner 25. A supply line 26 supplies g-as to said burner and has a control shut-off valve 27, which is pressure operated by means of a control diaphragm 28, connected therein. When the valve 27 is Iopen fuel gas may pass to the main burner 2S but when said valve is closed the main burner cannot operate. As will be explained, the pilot control device B directs a pressure through a conductor 33 to diaphragm 28 to maint-ain valve 27 open so long as the pilot flame F is applying heat to the detector assembly A; in the event that the flame F is extinguished, then pressure applied to diaphragm 28 is relieved, resulting in a closure of the shut-off valve 27 to render the main burner 25 inoperative.

It is preferable that the fuel for the pilot light flame F be supplied through a line 29 ywhich extends from the main gas supply line 26 at a point between the shut-off valve 27 and the main burner. In such case, closing of the Valve 27 by reason of extinguishing of the pilot light flame =F will result in shutting off a supply of gas to the pilot light.

As an additional safety feature it is also desirable to shut off the supply of pilot pressure to the pilot pressure control unit B when the main gas ilow is shut ofi by closure of the shut-off valve 27. As schematically illustrated, pilot pressure is supplied through a line 39 which has a three-way valve 31 connected therein; this Valve is actuated by an operating diaphragm 32 which is supplied with pressure through line 34, said line 34 connecting with the conductor 33 which supplies pressure to the diaphragm 28 of the shut-off valve. Normally, pressure acting on the diaphragm 32 of the three-way valve 31 maintains this valve in a position establishing communication between the pilot pressure supply line 30 and a conductor 33a which extends to the inlet side of control device B. When pressure is vented from the diaphragm 32 of the three-way control valve 31, said valve is actuated to close line 30 and establish communication between the conductor 33a and atmosphere, thereby resulting in bleeding of said conductor 33a. It is thus apparent that when the shut-oft` valve 27 is closed by reason of venting of the pressure in line 33 and also in line 34 communicating therewith, supply of fuel to both the main burner and the pilot light is shut off; at the same time, three-way valve 31 is operated to shut off the pilot pressure supply to the control device B and to vent inlet line 33a.

Although the control device B may take several diierent forms, o-ne type of pilot control unit which has been found satisfactory is illustrated. This unit includes a tubular housing 35 which has one end connected to the threads i3 of the body 10 and a chamber 36 is formed within the interior of the housing. The opposite end of the housing is closed except for a bore 35a within which a stem 37 is adjustably mounted for a purpose to be hereinafter explained. The stem is formed with a passage 37a which communicates in all adjusted positions of the stem with a pilot pressure inlet 38 provided in the body; said inlet has line 33a connected therewith. The inner end of the passage is in communication with the chamber and has a valve seat 37b formed thereon. The chamber 36 is in constant communication with the lines 33 and 34 through a passage 39 which may be formed in the body 1?. When pilot pressure from the inlet 38 enters the chamber 36 of housing 35, such pressure may pass through the passage 39, conductor 33 and line 34 to the diaphragms 23 and 32 of the shut-off valve 27 and the three-Way Valve 31, respectively. On the other hand, when pressure is vented from the chamber 36 through a vent passage 41 as will be explained, the pressure acting on said diaphragms 2S and 32 is released allowing valve 27 to close and causing the three-way valve 31 to shut off further pilot pressure supply.

For controlling the admission and release of pressure from the chamber 36 in accordance with the position of the actuating end 15a of the rod 15 of detector assembly A, a valve member 42 is provided. A ball valve 43, which is adapted to engage the seat 37b at one end of the passage 37a, is formed at one end of valve member 42 while a second ball valve 44 is secured to the opposite end thereof. Ball valve 44 is engageable with a valve seat member 45 which is mounted within one end of an inner tubular casing 46. The inner casing is disposed inside of a bellows 47 having one end sealed with the valve seat member 45 and its opposite end sealed with the end of the body 10 in surrounding relationship to the counterbore 112 of said body. The counterbore 12 thus communicates with the interior of the bellows and the vent passage 41 extends therefrom so that pressure from within the bellows may escape through said vent.

In the operation of the overall apparatus, the application of heat by the pilot light flame F will heat the temperature sensitive or responsive element T consisting of the actuating rod i5 and the sleeve or tube 16. By reason of the construction, as heretofore explained, tube 16 will elongate and will move the actuating rod in a direction to the right in FIGURE l. The end of the actuating rod is connected to the inner casing 46 and results in moving said casing in a direction to the right whereby the valve seat 45 acting on ball valve 44 will move the valve member 42 in a direction to unseat the ball 43 from seat 37b. Pilot pressure from the pilot pressure supply line 30 flows through three-way valve 3l. and conductor 33a to the inlet 3S; from this point pressure is directed into the chamber 36 and then passes through the passage 39 to the conductor 33 and line 34 to act upon the diaphragms 23 and 32 of the shut-off valve 27 and three-way valve 31, respectively. Therefore, so long as the heat is being applied to device A as heretofore described by reason of the pilot flame F, pilot pressure may flow to the inlet 38 of the pilot pressure control unit B and the valve 27 in the supply line 26 extending to the main burner 25 remains open.

In the event that the ame of the pilot light F is extinguished, heat is rapidly conducted from the element A, and this results in contraction of the sleeve or tube 16. Such contraction of the tube 16 moves the actuating rod 15 in a direction to the left in FIGURE 1 whereby the valve seat 45 is moved toward the passage 37; a coil spring 48 beneath the ball valve 44 causes the valve member 42 to follow the seat 45 until the ball valve 43 of said valve member engages the seat 37b. Continued motion of the actuating rod 15 results in unseating the ball valve 44 from the seat member 45 and when this occurs pressure in the lines 33 and 34 acting on diaphragms 28 and 32 llows back into the pressure chamber 36 and then through the valve seat member 45 into the interior of the bellows 47. From this point pressure ows through the counterbore 12 of housing llt) and escapes through the vent opening 41. As soon as pressure acting on diaphragm 2S is released, valve 27 is closed to shut olf further supply through the burner supply line 26. At the same time, further fuel supply to the pilot light is shut ot, and simultaneously therewith the three-way valve 31 is actuated to shut olf any further flow of pilot pressure to the pilot device B. The heater or furnace to which the apparatus is applied is therefore rendered completely inoperative, and, until such time as an operator relights the pilot ame F, the parts will remain in such position.

Upon relighting of the flame heat is again applied to the control device A, the temperature responsive element is reheated to impart movement to the rod 15 whereby pressure may again be directed to the diaphragms 28 and 32. Provision is made for pressuring up the diaphragm 32 to actuate valve 31 in order that pilot pressure may be supplied to unit B at the start of the operation. This initial pressure to diaphragm 32 is through line t) and includes a hand-operated valve 5l which would be closed after the apparatus is back on automatic operation. It is understood that the main burner gas supply line 26 has the usual automatically operated valve indicated at 52 also located therein; this automatically operated valve is normally responsive to the usual thermostatic controller unit generally indicated at 52a which controls the actuation of the main burner under varying load conditions.

The particular control unit B may be readily adjusted to adjust the temperature level at which the detector assembly operates to close the shut-ott` valve 27. The

adjustment of temperature level is important because at periods when the main burner is firing, the temperature level in the heater or furnace immediately surrounding the end of the temperature sensitive element may be substantially greater than when the burner is off; in other instances, the secondary air to the main burner may enter the tirebox in such manner that the temperature-sensitive element is cooled substantially below the temperature prevailing when the main burner is off. For these reasons, an arbitrary setting of the temperature level would produce unreliable operation.

The proper adjustment of the operating temperature level is accomplished by adjusting the stem 37 inwardly and outwardly of the housing 35 and chamber 36. Since the seat 37b at the inner end of the stern is arranged to be engaged with the ball 43 of valve member 42, the adjustment of the stern changes the position of the seat relative to the end 15a of the actuating rod 15; therefore, the rod must undergo more or less motion, as caused by the effect of reducing temperature on the temperature responsive element T, before the valve 43 is seated to vent conductor 34 and close shut-olf valve. The stem is readily available for adjustment by removal of a cap 37e and the adjustment may be made during one or more cycles of operation. ln this way the unit is accurately set for reliable operation in accordance with Cil the particular heater or furnace to which the same is applied.

Although a pressure operated control unit is illustrated the invention contemplates the use of any suitable controlling device for actuating the shut-olf valve 27. In other words, any well known type of control device may be combined with the detector assembly A and the invention is not to be restricted to the unit shown.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made Within the scope of the appended claims without departing from the spirit of the invention.

What I claim is:

l. A detector assembly for a pilot light safety control apparatus including, a body, an actuator carried by the body and mounted for movement relative thereto, a temperature sensitive element secured to and projecting from one end of the body and having connection with the actuator, whereby variations in temperature of the temperature sensitive element impart movement to said actuator, and heat-distributing means surrounding the temerature sensitive element substantially throughout its length in circumferential spaced relationship thereto to substantially enclose the same and being constructed of a material of high heat conducting capacity whereby the application of a pilot light name to one area of said means results in the distribution of heat along substantially the entire length of the temperature sensitive element.

2. A detector assembly as set forth in claim l, together with a heat resistant shield surrounding and enclosing the heat distributing means to protect the same against damage by the direct flame of a pilot light.

3. A detector assembly for a pilot light safety control apparatus including, a body, an actuator carried by the body and mounted for movement relative thereto, a temperature sensitive element secured to and projecting from one end of the body and having connection with the actuator, whereby variations in temperature of the temperature sensitive eiement impart movement to said actuator, a tubular heat conducting member surrounding the temperature responsive element substantially throughout its length in circumferential spaced relationship thereto, said member having a relatively thick wall area as compared to the wall thickness of the temperature sensitive element and being constructed of a material having high heat conducting capacity, and a thin walled shield constructed of heat-resistant material enclosing the heat conducting member and sealed therewith to prevent oxidation of the member when a pilot light llame is applied to the exterior of said shield.

4. A detector assembly for a pilot light safety control device including, a body, an actuating rod mounted in the body for movement relative thereto, one end of the rod extending outwardly from said body, a tube surrounding the projecting end of the actuating rod and having one end portion secured to the body with its opposite end secured to the outer projecting end of the actuating rod, the materials of said rod and said tube having different coeiicients of expansion whereby said rod and tube form a temperature responsive element, a tubular heat resistant shield encircling the temperature responsive element in spaced relation thereto and having one end secured to said body, and a tubular heat conducting sleeve constructed of a material having relatively high heat conducting capacity disposed within the shield and in encircling relationship to the temperature responsive element, said sleeve being slidable within limits within the bore of the shield, the application of heat to the exterior of the shield at one point thereof resulting in a heating of the heat conducting member which heat conducting member distributes said heat longitu- 9 dinally throughout the length of the temperature responsive element.

5. A detector assembly set forth in caim 4, Wherein the material of which one of the parts of the teinperature responsive element is Constructed comprises a low expansion alloy having a very low thermal coefficient of expansion within the tower temperature ranges and the material of which the other part is constructed is a stainless steel, the heat conducting capacity of the heat-conducting sleeve bearing such relationship to the applied heat that it will maintain the temperature of the part constructed of the low expansion alloy Within the lower temperature ranges where said part has a very low thermal coefficient of expansion.

6. A detector assembly for a pilot light safety control apparatus for a main burner including, a body, a ternpereture sensitive element capable of undergoing physical change due to temperature change secured to and projecting from one end of the body and exposed to a pilot light flame, means disposed between said temperature sensitive element and the arne and having its inner surface spaced from the surface of the temperature sensitive element to provide an air space therebetween for 10 continuously conducting heat away from that area of the temperature-sensitve element which is dire-etly exposed to the flame, and means for constantly dissipating the heat from said last-named means at a point removed from the area of heat application.

7. A detector assembly as set forth in claim 6, to gether with a tubular heat resistant shield enclosing the tempmature-sensitive element and the heat-conducting means for protecting the latter from damage by oxidation due to the gases and atmosphere in the area of heat appiioation.

Referenees Cited in the file of this patent UNTED STATES PATENTS 1,794,531 Newell Mar. 3, 1931 1,820,510 Tuck Aug. 25, 1931 1,902,451 Johnson Mar. 21, 1933 1,995,38 Foote Mar. 26, 1935 2,185,423 Anderson Ian. 2, 1940 2,348,965 Bougherty May 16, 1944 2,379,124- Wasson .une 26, 1945 2,381,215 Hahn Aug. 7, 1945 

1. A DETECTOR ASSEMBLY FOR A PILOT LIGHT SAFETY CONTROL APPARATUS INCLUDING, A BODY, AN ACTUATOR CARRIED BY THE BODY AND MOUNTED FOR MOVEMENT RELATIVE THERETO, A TEMPERATURE SENSITIVE ELEMENT SECURED TO AND PROJECTING FROM ONE END OF THE BODY AND HAVING CONNECTION WITH THE ACTUATOR, WHEREBY VARIATIONS IN TEMPERATURE OF THE TEMPERATURE SENSITIVE ELEMENT IMPART MOVEMENT TO SAID ACTUATOR, AND HEAT-DISTRIBUTING MEANS SURROUNDING THE TEMPERATURE SENSITIVE ELEMENT SUBSTANTIALLY THROUGHOUT ITS LENGTH IN CIRCUMFERENTIAL SPACED RELATIONSHIP THERETO TO SUBSTANTIALLY ENCLOSE THE SAME AND BEING CONSTRUCTED OF A MATERIAL OF HIGH HEAT CONDUCTING CAPACITY WHEREBY THE APPLICATION OF A PRIOR LIGHT FRAME TO ONE AREA OF SAID MEANS RESULTS IN THE DISTRIBUTION OF HEAT ALONG SUBSTANTIALLY THE ENTIRE LENGTH OF THE TEMPERATURE SENSITIVE ELEMENT. 